Brake system with pump power consumption control

ABSTRACT

A hydraulic brake system with anti-lock control and traction slip control has an electric-motor-driven hydraulic pump 6 and a motor 7 for auxiliary pressure supply during a controlled braking operation and during a traction slip control operation by way of brake management. During a traction slip control operation the speed of the hydraulic pump is reduced by way of a reduction in the power consumption of the drive motor of the pump down to a predetermined value where the speed and the noise development are low relative to values with nominal capacity. The power limitation will be cancelled in situations critical to safety and reliability or in case of certain malfunctions of the control system. The power limitation is achieved by way of relays and an ohmic series resistor or by way of a so-called semiconductor relay or electronic relay.

BACKGROUND OF THE INVENTION

The present invention relates to a hydraulic brake system having: (1)anti-lock control and/or traction slip control, (2) anelectric-motor-driven hydraulic pump for auxiliary pressure supplyduring a controlled braking operation and during a traction slip controloperation by means of brake management, and (3) an electronic controlunit for controlling the auxiliary pressure and for modulating orcontrolling the braking pressure in the wheel brakes of the controlledwheels in dependence on the rotational behavior of the wheels and/or onsignals representing the proper operation of the brake system and of theelectronic elements or pointing out malfunctions.

Hydraulic brake systems that are known and provided with electronicanti-lock control and traction slip control are equipped with aone-circuit or multi-circuit hydraulic pump for auxiliary pressuresupply. Usually, electric-motor-driven pumps are used that are turned onby the associated electronic control unit upon the onset of control. Thehydraulic energy consumption varies very much depending on the controloperation and control phase. The nominal capacity of the motor-and-pumpunit, of course, is arranged to handle the maximum demand that mayappear in certain situations during an anti-lock control operation. Asregards traction slip control by means of brake management, where thepump is to deliver the pressure for the application of the brake, lessenergy and less hydraulic pressure, in principle, are needed as comparedwith anti-lock control. For cost reasons, the same unit is used foranti-lock control and traction slip control, although a smaller, lesspotential motor-and-pump unit would be sufficient for traction slipcontrol.

The noise developed upon the onset of control and caused by theturning-on or rather by the operation of the hydraulic pump, however, isfelt as a disturbance, namely a reduction in driving comfort, during atraction slip control operation.

SUMMARY OF THE INVENTION

Therefore, it is an objective of the present invention to reducedecisively these troublesome noises in a simple manner incurring aslittle expenditure as possible. In achieving this aim, however,operational reliability is not to be reduced even in unfavorablesituations.

It has been found that this object is achieved by arranging a brakesystem of the type referred to above, so that during a traction slipcontrol operation, the speed of the hydraulic pump or rather of the pumpmotor is reduced by limiting the power consumption of the drive motor toa predetermined value where the speed and the noise development aresmall relative to the noise development with nominal capacity. Inaddition, the control unit will cancel the power limitation insituations critical to safety and reliability or in case of certainmalfunctions of the control system. The speed limitation is expedientlycontrolled by the electronic control unit or by additional circuitry.

In accordance with the present invention, there is, thus, a limitationof the current consumption and, hence, of the power consumption of thedrive motor of the hydraulic pump in case of a traction slip controloperation, thereby considerably reducing the mainlymotor-speed-dependent noise development to a level which no longer willbe felt to be troublesome or, at most, minimally so. In practice, aspeed of 40% to 60% of the nominal speed is sufficient during tractionslip control. In situations critical to safety and reliability, such asin case of insufficient supply voltage, extreme outside temperaturesetc., the power limitation is cancelled. Consequently, noise reductionis achieved without any losses as regards the safety and reliability ofthe controlled brake system.

In accordance with an advantageous embodiment of the present invention,which is characterized by particularly low manufacturing expenditure, anohmic resistor is inserted into the electric attachment of the pumpmotor in order to limit the power consumption, with the ohmic resistorbeing bridged by the contact of a relay, controlled by the electroniccontrol unit, in case of full power consumption.

Also in accordance with the present invention, instead of the ohmicresistor, it is possible to use a controllable resistor, such as asemiconductor relay, switching transistor or the like, which isactuatable by means of an electronic-control-unit-generated pulsesequence in order to limit the power consumption of the hydraulic pumpor rather the power consumption of the motor-and-pump unit. If actuatedby a permanent signal, the intrinsic impedance of such a controllableresistor will become so small as to be negligible.

In the last-mentioned embodiment, it is also possible to adapt the powerconsumption of respectively the hydraulic pump and electric motorexactly to the respective demand by means of modulating the pulsesequence serving to actuate the variable resistor.

Further, in accordance with another embodiment of the present invention,upon the onset of control, the motor of the hydraulic pump, at first, isactuated with full power and that, only after a predetermined period,such as of 100 msec to 500 msec, the power consumption of the electricmotor is limited to a sufficient extent to ensure that the motor willrun at a reduced speed and will produce but a low noise.

Further characteristics, advantages and applications of the presentinvention will become evident from the following description of furtherdetails, reference being made to the accompanying drawing which, by wayof a diagram of the fundamental principles, represents the maincomponents of an inventive brake system which are necessary forunderstanding this invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a preferred embodiment of the present invention.

FIG. 1A represents alternative arrangements of the power limiting means.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing, a brake system, having anti-lock control andtraction slip control in accordance with the present invention, includesa master cylinder 1, a brake booster 2, a pressure compensation andstorage reservoir 3 and a braking pressure modulator 4. Moreover, thereis a motor-and-pump unit 5 composed of a hydraulic pump 6 and anelectric drive motor 7 for auxiliary pressure generation. As there aretwo hydraulically separated brake circuits I, I', II, II' to which twovehicle wheels, at a time, are connected, it is possible to use ahydraulic pump with two hydraulically separated circuits instead of pump6. Brake systems of this type are generally known and are, therefore,not illustrated here.

An electronic control unit 8 also is included in a brake systemconstructed in accordance with the present invention. This electroniccontrol unit 8 serves to evaluate the information about the rotationalbehavior of the wheels contained in signals developed by wheel sensorsS₁ through S₄ and to generate braking pressure control signals. Thebraking pressure control signals are supplied to the braking pressuremodulator 4 via lines represented by a multiple line 9. These controlsignals serve to control solenoid valves which, depending on the controlphase, keep the pressure in the wheel brakes constant, reduce thepressure and reincrease the pressure. In case of traction slip control,at first, the pressure medium path from the wheel brakes to the mastercylinder 1 will be locked by means of such solenoid valves.Subsequently, by means of the hydraulic pump 6, the desired brakemanagement will be performed in order to stabilize the spinning wheels.V_(CC) represents the attachment of the power supply to the electroniccontrol elements.

In the illustrated FIG. 1 embodiment of the present invention,characterized by particularly low manufacturing expenditure, the powerlimitation during a traction slip control operation is achieved by anohmic series resistor R_(V). To this end, the switching contacts a and bof two relays A, B, respectively, are inserted into the electricconnection path of the electric motor 7, i.e., in the path to thebattery or voltage source U_(B). The two relays A, B are directlycontrolled by the electronic control unit 8. Relay A is the actual motorrelay, so that the motor 7 of the motor-and-pump unit 5 can be turned onand off via the switching contact of this relay.

In case of an anti-lock control operation, possibly in dependence on theactual auxiliary hydraulic energy demand, motor relay A will beactuated. It is of no importance whether the switching contact b ofauxiliary relay B will likewise become closed or will stay open in thisphase.

During a traction slip control operation, however, according to thepresent invention, only auxiliary relay B will be actuated. The seriesresistor R_(V) in the connection path from the battery U_(B) to theelectric motor 7 of the pump 6 will limit the power consumption of thiselectric motor 7 and its speed to 40% to 60%, for example, of thenominal speed. The switching contact a of the motor relay A will stayopen.

Upon the onset of a traction slip control operation, in many cases, itis advantageous to excite both relays A and B for a short period atfirst in order to accelerate the start-up of the motor 7 or rather ofthe motor-and-pump unit 5. Then, after a predetermined time, such as 100msec to 500 msec, the relay A is turned off, so that the power issupplied to the motor 7 only via the series resistor R_(V).

According to the present invention, the power limitation achieved bydirecting the motor supply current via the series resistor R_(V) iscancelled in situations critical to safety and reliability caused, forexample, by certain defects, by a drop in the battery voltage U_(B), byparticularly low outside temperatures and the like. For the embodimentof the invention illustrated, this occurs by actuating the motor relayA.

The necessary information is supplied to the control unit 8 via theinputs E_(m), E_(n), E_(p) in order to recognize such situationscritical to safety and reliability. This information is obtainable, forexample, by means of equipment monitoring the voltage, by means ofcorresponding sensors and the like, with many arrangements beingpossible. One example of such equipment for monitoring the system forsituations critical to safety and reliability includes a speed sensor12. Sensor 12 measures the actual speed in rpm of the drive motor 7 andsignals the control unit 8 a drop in the speed below a critical value,whereupon the control unit 8 will cancel the power limitation. Such adrop in the speed of the motor below a limit value can be caused by aparticularly high load on the motor-and-pump unit, by an unusually lowbattery voltage U_(B), by a defective contact b or by a defectiveauxiliary relay B to mention but a few examples.

Instead of using the contact configuration, inclusive of the seriesresistor R_(V), the whole of which is marked by reference numeral 10, inFIG. 1 it is also possible, according to the present invention, to use aso-called semiconductor relay or an electronic relay or a switchingtransistor representing a controllable resistor. Such alternatives arerepresented in FIG. 1A by a block 10', including a variable resistorR_(v) ', and a signal line 11. In this case, the necessary controlsignals that likewise can be generated in the control unit 8 aresupplied to the electronic relay 10' via signal line 11. Such anelectronic motor relay, at present, is more expensive than theillustrated relay configuration 10 of FIG. 1. However, it has theadvantage that, by controlling the resistor by means of a pulsesequence, it is possible to achieve a practically loss-free control ofthe motor 7. By means of such an electronic relay, it is also possibleto adapt the power consumption, or rather the power limitation of themotor 7, with a much higher degree of precision and in several stages tothe actual demand by modulating the actuating pulse sequence. In manycases, however, the described and represented two-stage actuation of themotor 7, or rather the speed reduction, by means of the insertion of theseries resistor R_(V) will be sufficient in order to achieve the desiredobjective, namely a sufficient reduction of the disturbing noises of themotor-and-pump unit 5. What is decisive is that the demanded operationalreliability of the brake system will be kept up by monitoring andcancelling the power limitation in situations critical to safety andreliability. For critical situations, the principle of safety firstbefore comfort holds.

We claim:
 1. A hydraulic brake system with anti-lock control andtraction slip control, with an electric-motor-driven hydraulic pump forauxiliary pressure supply during a controlled braking operation andduring a traction slip control operation by means of brake management,with an electronic control unit for controlling the auxiliary pressureand for modulating or controlling the braking pressure in the wheelbrakes of controlled wheels in dependence on the rotational behavior ofthe wheels and/or on signals representing predetermined operation of thebrake system and of the electronic elements or pointing outmalfunctions, characterized in that, during the traction slip controloperation, the speed of the hydraulic pump is reduced by limiting thepower consumption of a pump motor to a predetermined value where thenoise development is small relative to the noise development withnominal capacity; and in that the electronic control unit cancels thepower consumption limitation in situations critical to safety andreliability or in case of malfunctions of the control system.
 2. A brakesystem as claimed in claim 1, characterized in that an ohmic resistor isinserted into an electric attachment of the pump motor in order to limitthe power consumption, said resistor being bridged by the contact of arelay, controlled by the electronic control unit, in case of full powerconsumption.
 3. A brake system as claimed in claim 1, characterized inthat a controllable resistor is inserted into the electric attachment ofthe pump motor for the purpose of respectively controlling or limitingthe power consumption of the pump motor, is actuatable by means of apulse sequence generated by the electronic control unit.
 4. A brakesystem as claimed in claim 3, characterized in that an electronic relayor a semiconductor relay, or a switching transistor is provided as thecontrollable resistor.
 5. A brake system as claimed in claim 4characterized in that, by modulating the pulse sequence which serves toactuate the controllable resistor, the electronic control unit adaptsthe power consumption of the motor of the hydraulic pump to therespective demand of the motor.
 6. A brake system as claimed in claim 3characterized in that, by modulating the pulse sequence which serves toactuate the controllable resistor, the electronic control unit adaptsthe power consumption of the motor of the hydraulic pump to therespective demand of the motor.
 7. A brake system as claimed in claim 1,characterized in that the electronic control unit cancels the powerlimitation upon a drop in the supply voltage below a limit value.
 8. Abrake system as claimed in claim 1, characterized in that the electroniccontrol unit monitors the control variation such as the rotationalbehavior of the wheels in order to detect situations critical to safetyand reliability.
 9. A brake system as claimed in claim 1, characterizedin that the electronic control unit monitors the speed of the pump motorin order to detect situations critical to safety and reliability.
 10. Abrake system as claimed in claim 1, characterized in that the powerlimitation upon the turning-on of the hydraulic pump comes on after apredetermined time period such as of 100 msec to 500 msec.
 11. Ahydraulic brake system having anti-lock control and traction slipcontrol for controlling a plurality of wheel brakes associated with aplurality of wheels of a vehicle, said brake system comprising:firstsignal means for supplying a first set of signals representative of therotational behavior of the wheels; second signal means for supplying asecond set of signals representative of proper operation of selectedcomponents of said brake system and of malfunctions of said selectedcomponents; wheel brake control means for controlling pressure fluidflow to and from the wheel brakes; an electric-motor-driven hydraulicpump for supplying auxiliary fluid pressure to said wheel brakes duringan anti-lock control operation and during a traction slip controloperation; power control means for limiting power consumption by saidelectric-motor-driven hydraulic pump to reduce the speed of saidelectric-motor-driven hydraulic pump to a predetermined value at whichnoise development is small relative to noise development at nominalspeed during traction slip control operation; and electronic controlmeans for developing:(1) first control signals in response to said firstset of signals for controlling:(a) said wheel brake control means andsaid electric-motor-driven hydraulic pump during anti-lock controloperation, and (b) said wheel brake control means and said power controlmeans during traction slip control operation, and (2) second controlsignals in response to said second set of signals for controlling saidpower control means to cancel the power limitation in at least one ofthe following situations:(a) critical to safety, (b) critical toreliability, and (c) in case of malfunctions of any of said selectedcomponents of said brake system.
 12. A brake system according to claim11 wherein said power control means include an ohmic resistor and arelay controlled by said second control signals and having a contactbridging said ohmic resistor when closed in response to said secondcontrol signals.
 13. A brake system according to claim 11 wherein saidpower control means include a controllable resistor controlled inresponse to said second control signals.
 14. A brake system according toclaim 13 wherein said controllable resistor is a semiconductor relay.15. A brake system according to claim 14 wherein said semiconductorrelay is actuated by a pulse sequence modulated by said electroniccontrol means.
 16. A brake system according to claim 13 wherein saidcontrollable resistor is a switching transistor.
 17. A brake systemaccording to claim 16 wherein said switching transistor is actuated by apulse sequence modulated by said electronic control means.
 18. A brakesystem according to claim 13 wherein said controllable resistor is anelectronic relay.
 19. A brake system according to claim 18 wherein saidelectronic relay is actuated by a pulse sequence modulated by saidelectronic control means.
 20. A brake system according to claim 13wherein said controllable resistor is actuated by a pulse sequencemodulated by said electronic control means.
 21. A brake system accordingto claim 11 wherein said electronic control means cancels the powerlimitation upon a drop in the supply voltage below a limit value.
 22. Abrake system according to claim 11 wherein said electronic control meansdevelops an indication of vehicle reference speed from said first set ofsignals representative of the rotational behavior of the wheels todetect situations critical to safety and reliability.
 23. A brake systemaccording to claim 11 wherein said electronic control means monitor thespeed of said electric-motor-driven hydraulic pump to detect situationscritical to safety and reliability.
 24. A brake system according toclaim 11 wherein actuation of said power control means to effect thepower limitation upon said electric-motor-driven hydraulic pump isdelayed a predetermined period of time.
 25. A brake system according toclaim 24 wherein said predetermined period of time is 100 msec to 500msec.